1. Field of the Invention
The present invention relates to a film deposition method.
2. Description of the Related Art
Recently, a requirement of increasing the memory capacity of a semiconductor memory device has been increased. Thus, a high dielectric material has been used for an insulating layer of a memory cell of the high dielectric semiconductor memory device. For one of such materials, zirconium oxide (ZrO) is known. ZrO has a relative dielectric constant of around 24 to 40, however, ZrO has a problem that a withstand voltage is low. Thus, in order to increase the withstand voltage, aluminum (Al) is added to ZrO (Patent Document 1 and Patent Document 2, for example).
In order to reduce a cost of manufacturing a semiconductor memory device, a semiconductor wafer (hereinafter simply referred to as a “wafer”) with a larger diameter has been used. With this, it is necessary to improve across-the-wafer uniformity. In accordance with such a requirement, a film deposition method so-called “Atomic Layer Deposition” (ALD) or “Molecular Layer Deposition” (MLD) is expected. In ALD, a thin film of a reaction product is formed on a surface of a wafer by repeating a cycle in which a reaction gas A is adsorbed onto the surface of the wafer, and the adsorbed reaction gas A is reacted with another reaction gas B which reacts with the reaction gas A. As ALD uses adsorption of reaction gasses onto a surface of a wafer, there are advantages in ALD that the thickness across-the-wafer uniformity can be obtained and the thickness can be preferably controlled.
When ALD is performed in a vertical batch film deposition apparatus, first, a reaction gas A is introduced into a process tube chamber in which plural wafers are placed for a predetermined period to have the reaction gas A adsorbed onto the surface of the wafer. Then, the reaction gas A is evacuated from the process tube chamber while supplying a purge gas to purge the reaction gas A from the process tube chamber. Subsequently, a reaction gas B is introduced into the process tube chamber for a predetermined period to have the reaction gas A and the reaction gas B react on the surface of the wafer so that a reaction product is formed on the surface of the wafer. These steps are repeated until a thin film with a predetermined thickness is formed.
When ALD is performed in the batch film deposition apparatus, as described above, supplying of the reaction gas A, evacuation/purging of the reaction gas A, supplying of the reaction gas B, and evacuation/purging of the reaction gas B are performed. Thus, the process time becomes long as it is necessary to change the reaction gas A and the reaction gas B to be introduced and evacuation/purging are performed between changing the reaction gasses.
On the other hand, a film deposition apparatus with a turntable is known. Such a film deposition apparatus includes a turntable which is rotatably provided in a vacuum chamber, a supplying area of the reaction gas A, a supplying area of the reaction gas B, and separation areas for separating the supplying areas, respectively, provided above the turntable, evacuation ports corresponding to the supplying areas of the reaction gas A and the reaction gas B, respectively, and evacuation devices connected to the evacuation ports, respectively.
In such a film deposition apparatus, plural wafers mounted on the turntable pass the supplying area of the reaction gas A, the separation area, the supplying area of the reaction gas B, and the separation area in this order by rotating the turntable. With this, the reaction gas A is adsorbed onto the surface of the wafers at the supplying area of the reaction gas A, and the reaction gas A and the reaction gas B are reacted at the supplying area of the reaction gas B. Therefore, it is unnecessary to change the supplying of the reaction gas A and the reaction gas B while depositing the film and the reaction gas A and the reaction gas B can be continuously supplied. Thus, the evacuation/purging steps are unnecessary to reduce the process time.
When forming a ZrO film to which aluminum (Al) is added (which will be referred to as an “Al doped ZrO film” hereinafter) using the film deposition apparatus with the turntable, Al can be doped into ZrO by mixing a reaction gas containing Zr (Zr source gas) and a reaction gas containing Al (Al source gas) in a pipe. However, at this time, if the Zr source gas and the Al source gas are supplied onto the wafer before being mixed to be a uniform concentration, the added amount of Al cannot be made uniform in-plane on the wafer.
Further, the Al doped ZrO film can be formed by controlling supplying of the Zr source gas and the Al source gas so that an AlO film is inserted between ZrO films. However, this may cause a difference in the added amount of Al between plural wafers or within each of the wafers based on the supply timing of the Al source gas.
Further, when adding Al to ZrO, although the withstand voltage is improved, the relative dielectric constant tends to become lower. Thus, it is necessary to add a slight amount of Al to ZrO while maintaining across-the-wafer uniformity.